The present invention relates generally to internal combustion engines, and more particularly to an air-cooled engine having a so-called side-valve arrangement and a cross-over intake manifold.
At present, single-cylinder air-cooled engines with a side valve configuration have a crankshaft and camshaft which are parallel to one another, with the camshaft being gear driven by the crankshaft. The combustion chamber overlies the piston and adjacent side valves and the engine cylinder extends perpendicular to the crankshaft. The valves lie parallel to the cylinder and directly overlie the camshaft which they engage. One valve is located above a horizontal plane extending through the center line of the cylinder, and the other valve is located below the plane, but both valves are side-by-side on the same side of the engine.
With this engine geometry, the exhaust and intake ports are limited to a configuration in which the intake and exhaust ports are located on the valve side of the engine and directed away from the bore in planes perpendicular to the crankshaft, or else directed away from the bore in opposite directions in a common plane through the valve centers and parallel to the crankshaft. The latter configuration involves an upper inlet and downward discharge. With both the intake and exhaust ports on the same side of the engine, a separate manifold must be used on either the carburetor or muffler to separate these units, since the exhaust heat and space configuration will affect the function of the carburetor.
It is therefore advantageous to separate the intake and exhaust ports, preferably on opposite sides of the cylinder bore, which allows for direct port mount of the muffler to the block and does not limit the size of the muffler since no carburetor is mounted on the muffler side of the engine.
Usually when the aforementioned split configuration is used the carburetor is placed on the opposite side of the bore from the valves, with a separate intake manifold to cross over from the valve side of the engine. Another approach for a split configuration is to cross over with the exhaust below the bore from a down discharge configuration with a stamped steel exhaust manifold.
Because the cross-over manifold must traverse the perimeter of the cylinder, the cross-over passage must follow a curved route in order to get around the cylinder bore and connect to the valve. A curved passage is difficult to cast integrally with the engine block because a curved interior casting core usually cannot be removed non-destructively. Therefore, it is known to employ a tube-type cross-over manifold which is separately assembled to an elbow fitting to accomplish the necessary curved passageway.
It is also known to provide a curved cross-over intake manifold which is cast in place integrally with the engine block, but with an opening or window in a portion of the passageway to provide for removal of the casting core. The opening or window is closed by a separate cover which is assembled to the casting.
Another known approach for providing an integrally cast cross-over passageway involves providing a curved hollow metal tube as a casting core which remains in place in the casting. The ends of the tube are machined open subsequent to casting to provide the cross-over manifold.
It would be desireable to provide an improved engine arrangement in which the cross-over manifold is cast in its entirety integral with the engine block casting under conventional casting techniques involving removable and reusable casting cores.
The present invention provides this and other desireable advantages.